Presenter(s): Geena Littel − Geophysics
Faculty Mentor(s): Amanda Thomas
Poster 1
Research Area: Natural/Physical Science
Funding: UO Department of Earth Sciences: Walter Youngquist Fellowship, James C. Stovall Fellowship, UROP VPRI Fellowship, UROP Mini Grant
In addition to fast, seismic slip during an earthquake, many subduction zones also host slow, largely aseismic slip. These “slow earthquakes” occur on timescales of weeks to months and are often accompanied by a weak seismic signal known as “tectonic tremor,” or simply “tremor.” Tremor behaves differently than regular earthquakes in that it is comprised of many small earthquakes that radiate low-frequency seismic energy and originate at the plate interface downdip of where large earthquakes typically occur. Ground-motion prediction equations (GMPEs) quantify ground-motion during an earthquake, and employ estimates of seismic-wave attenuation, that is, the decrease in amplitude of seismic waves as a function of distance from the earthquake source. Because tremor occurs frequently when compared to regular earthquakes in Cascadia, it presents an opportunity to better refine attenuation parameters for use in GMPEs. Here we quantify seismic-wave attenuation by performing an inversion using tremor ground motion amplitudes from three tectonic tremor episodes to determine the extent of regional variations and frequency dependence of seismic-wave attenuation in Cascadia. Inversion refers to the process of using tremor ground motion amplitudes, and a mathematical formulation relating seismic-wave amplitude and other known parameters, to solve for the unknown parameter- in this case, attenuation. Due to the large amount of tremor data, we can resolve spatial variations in the attenuation parameter along strike in Cascadia. As well, tectonic tremor exhibits the frequency dependence expected for attenuation, as seen in GMPEs developed from moderate to large magnitude earthquakes. Hence, tectonic tremor can be used to provide insight into the geological and physical factors manifested in attenuation and refine estimates of attenuation for ground-motion prediction, thus having important implications for hazard assessment.